Bendix Diagnoses Common Car Brake Issues

Braking systems are intricate, comprising numerous moving components that endure harsh conditions, including extreme temperatures. Add challenging road surfaces and debris into the mix, and it's unsurprising that braking issues may arise, particularly when maintenance is overlooked.

Some faults are easier to identify than others; here are several of the most common.

Noise related 

Given the various moving parts within the braking system, and that components such as brake pads and brake shoes make contact with rotors and brake drums with force, it’s difficult to eliminate noise completely but the noise should not be excessive or overwhelming. 

Squealing brakes are often caused when friction materials (brake pads or brake shoes) contact the disc rotor/caliper or brake shoe causing vibration. The noise could be caused by poorly lubricated components including caliper hardware such as pins, slides and bushes; brake pad backing plates; brake shims and other metal-to-metal or metal-to-rubber contact paints. This noise may also indicate a scored rotor surface or that the friction material is badly worn, with metal-on-metal contact occurring.

Changes in pedal feel

Certain braking system issues can be felt by the driver at the brake pedal. A soft or spongy pedal can mean that there’s air in the brake lines or the brake fluid is very low. Other causes could include a damaged or leaking brake booster or brake master cylinder meaning it won’t maintain sufficient hydraulic pressure in the system.

If the brake pedal is difficult to push, this could be caused by a malfunctioning brake booster. The brake booster multiplies the force at the brake pedal to something much greater by the time the pads and shoes bite at the rotors or drums, so if not working correctly the driver will need to push on the brake pedal much harder.

Vibrations or pulses through the brake pedal are other symptoms of an issue. Pulsation is normally caused by Disc Thickness Variation (DTV) or warped rotors. DTV can occur if disc brake rotors haven’t been installed correctly – perhaps because of uneven lug nut torque, damaged studs or debris between the hub and rotor – and lateral rotor run-out can occur. This causes side-to-side movement as the rotor rotates rather than the rotors circulating through an even plane.

Warping occurs when the rotor surface becomes uneven and is often caused by excessive heat. Through regular high-load braking situations, the rotors become glazed from the brake pad materials rubbing off on the rotor at extreme temperatures.

Extreme temperature changes can also cause warping. For example, heavy braking followed by submersion in cold water might be experienced off-road when four-wheel driving.

Reduced braking performance

A noticeable reduction in braking performance should be taken very seriously and addressed immediately. Brakes should quickly and efficiently slow the vehicle up in a straight line with minimal effort when in the correct working order.

A vehicle that pulls to one side under braking normally signals an imbalance within the system and could be caused by a sticking brake caliper. The root problem may link back to poor caliper slide pin lubrication or corrosion/debris at the caliper piston(s) which causes the caliper to drag.

Needing a longer stopping distance can also be caused by worn disc brake pads or brake shoes – the thinner the friction material becomes, the less effective braking becomes.

In certain conditions and driving environments brakes can also experience a temporary reduction in performance, this is known as brake fade. Brake fade is caused by the added heat generated from repeated or sustained braking, or braking under heavy loads. When the heat doesn’t effectively dissipate, the braking becomes compromised.  

Drivers can minimise brake fade by ensuring the braking system is in good order; upgrading some components should also be considered if the vehicle is regularly used when brakes are working hard. They can also adapt their driving style to put less pressure on the brakes.

Another factor that can affect performance is old brake fluid. Over time brake fluid can absorb small amounts of moisture through imperfect seals, microscopic holes in rubber hoses or even if the cap is left off the brake fluid reservoir for too long. 

This moisture can gradually mix with the brake fluid increasing its water content and impacting the pressure from the brake pedal to the calipers or drums, potentially lowering the fluid's boiling point. High temperatures exacerbate the issue, especially during strenuous driving situations like towing.